;(function(win, lib) {
  var doc = win.document
  var docEl = doc.documentElement
  var metaEl = doc.querySelector('meta[name="viewport"]')
  var flexibleEl = doc.querySelector('meta[name="flexible"]')
  var dpr = 0
  var scale = 0
  var tid
  var flexible = lib.flexible || (lib.flexible = {})
   
  if (metaEl) {
   console.warn('将根据已有的meta标签来设置缩放比例')
   var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/)
   if (match) {
    scale = parseFloat(match[1])
    dpr = parseInt(1 / scale)
   }
  } else if (flexibleEl) {
   var content = flexibleEl.getAttribute('content')
   if (content) {
    var initialDpr = content.match(/initial\-dpr=([\d\.]+)/)
    var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/)
    if (initialDpr) {
     dpr = parseFloat(initialDpr[1])
     scale = parseFloat((1 / dpr).toFixed(2))
    }
    if (maximumDpr) {
     dpr = parseFloat(maximumDpr[1])
     scale = parseFloat((1 / dpr).toFixed(2))
    }
   }
  }
   
  if (!dpr && !scale) {
   var isAndroid = win.navigator.appVersion.match(/android/gi)
   var isIPhone = win.navigator.appVersion.match(/iphone/gi)
   var devicePixelRatio = win.devicePixelRatio
   if (isIPhone) {
    // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
    if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
     dpr = 3
    } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)) {
     dpr = 2
    } else {
     dpr = 1
    }
   } else {
    // 其他设备下，仍旧使用1倍的方案
    dpr = 1
   }
   scale = 1 / dpr
  }
   
  docEl.setAttribute('data-dpr', dpr)
  if (!metaEl) {
   metaEl = doc.createElement('meta')
   metaEl.setAttribute('name', 'viewport')
   metaEl.setAttribute(
    'content',
    'initial-scale=' +
     scale +
     ', maximum-scale=' +
     scale +
     ', minimum-scale=' +
     scale +
     ', user-scalable=no'
   )
   if (docEl.firstElementChild) {
    docEl.firstElementChild.appendChild(metaEl)
   } else {
    var wrap = doc.createElement('div')
    wrap.appendChild(metaEl)
    doc.write(wrap.innerHTML)
   }
  }
   
  function refreshRem() {
   var width = docEl.getBoundingClientRect().width
   if (width / dpr > 540) {
    width = 540 * dpr
   }
   var rem = width / 10
   docEl.style.fontSize = rem + 'px'
   flexible.rem = win.rem = rem
  }
   
  win.addEventListener(
   'resize',
   function() {
    clearTimeout(tid)
    tid = setTimeout(refreshRem, 300)
   },
   false
  )
  win.addEventListener(
   'pageshow',
   function(e) {
    if (e.persisted) {
     clearTimeout(tid)
     tid = setTimeout(refreshRem, 300)
    }
   },
   false
  )
   
  if (doc.readyState === 'complete') {
   doc.body.style.fontSize = 12 * dpr + 'px'
  } else {
   doc.addEventListener(
    'DOMContentLoaded',
    function(e) {
     doc.body.style.fontSize = 12 * dpr + 'px'
    },
    false
   )
  }
   
  refreshRem()
   
  flexible.dpr = win.dpr = dpr
  flexible.refreshRem = refreshRem
  flexible.rem2px = function(d) {
   var val = parseFloat(d) * this.rem
   if (typeof d === 'string' && d.match(/rem$/)) {
    val += 'px'
   }
   return val
  }
  flexible.px2rem = function(d) {
   var val = parseFloat(d) / this.rem
   if (typeof d === 'string' && d.match(/px$/)) {
    val += 'rem'
   }
   return val
  }
 })(window, window['lib'] || (window['lib'] = {}))